A mobile offshore drilling unit (MODU) performs drilling of a subsea well while maintaining a position over the well during operations. The drilling unit can be a drillship, a semisubmersible, a jack-up, and other movable offshore facility. The drilling unit may include self-propulsion equipment and require dynamic positioning or mooring equipment to maintain its position.
For example, the drilling unit may use a dynamic positioning system to accurately maintain position over the well, which is vital during operations. The positioning system requires multiple position inputs in order to operate correctly and reliably. These positions inputs are supplied by multiple positioning reference systems, including Global Navigation Satellite Systems (GNSS) and multiple Acoustic Positioning Reference Systems that supply X, Y and Z position coordinates. Recently, vessels have begun to also use Inertial Navigation systems (INS) in addition to the traditional positioning reference systems.
As an example, a dynamic positioning system of the prior art uses INS systems that work in tandem with traditional positioning reference systems. As is known, the INS systems require position updates in order to maintain an accurate position calculation over a long period of time. Currently, operating these systems in tandem involves using one INS system with one navigation satellite system and using another INS system with an acoustic system to provide inertial positions as well as more accurate and reliable positions for the positioning reference systems. The robustness of the system may be boosted by using a number of standalone positioning reference systems, such as navigation satellite systems and acoustic systems. These standalone systems may not be as accurate or precise so the dynamic system may apply less significance to their inputs.
Although the dynamic system using INS systems as noted above may be useful, operators seek to mitigate the risk of position loss due to a failure in station-keeping equipment as the failure can lead to significant detrimental effects. For this reason, operators are constantly looking for any technology that will increase the reliability of their operation. The impact of this cannot be overstated. Accordingly, what is needed is a dynamic positioning system that utilizes Inertial Navigation technology for a reference system configuration that maximizes the robustness of position inputs. The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.